The present invention relates to a technique for recording and reproducing signals recorded in a digital disc.
There are DVD-R/RW as formats of optical discs for recording and reproducing information. The primary feature of these formats lies in the address information required for identifying the address in recording and reproducing information which is formed on land portions of the disc in order to improve compatibility with the DVD-ROM format. A track is a region of the optical disc in which the information to be reproduced is recorded as marks. The address information is formed at the space section (also called the land) between guiding grooves (also called grooves) of the disc, to which information to be reproduced is recorded. This address is also called “land pre-pit address” or “LPP address.” At the time of tracking the recorded track(s), tracking detectors of the apparatus-detect the incident light and generate a plurality of signals representing light amount (hereinafter referred to as “light amount signal(s)”). The address information is detected based on a differential signal which is taken from the difference of light amount signals. The secondary feature of the above-mentioned format is wobbles provided in the optical disc, in which the guiding grooves are oscillated in the radial direction of the disc by a predetermined frequency. The wobble signal obtained based on the wobble is used as a reference signal for generating clocks for recording and reproducing the information. Same as address information detection, the wobble is also detected based on the differential signal which is taken from the difference between light amount signals.
Referring now to FIGS. 8 and 9A-9F, the configuration and operation of a conventional optical disc apparatus will be described.
FIG. 8 is a block diagram of a conventional optical disc apparatus 80 which records/reproduces information to/from a DVD-R/RW disc 101. The optical disc apparatus 80 comprises a disc motor 102, an optical head 103 that has focusing detectors, a reproduction signal detector, and tracking detectors for detecting light, a servo signal/reproduction signal generating circuit 104 for generating a focus error signal, tracking error signal, and reproduction signal based on the light amount signals from the detectors, a focus/tracking control section 105 for allowing the optical head 103 to keep tracking guiding grooves of the optical disc 101 using the output signal of the servo signal/reproduction signal generating circuit 104, a differential amplifying, circuit 106 for generating wobble signal/land pre-it address signal from the light amount signals of the tracking detectors of the optical head 103, a band pass filter 107 for extracting the wobble signal component from the output signal of the differential amplifying circuit 106, a wobble signal binary-coding circuit 108 for binarizing a wobble signal, which is an output signal of the band pass filter 107, and a wobble PLL circuit 109 . for generating clocks required for recording/reproducing the information recorded on the disc 101 from the wobble binary-coded signal.
Furthermore, the optical disc apparatus 80 comprises an amplitude detecting circuit 110 for detecting the amplitude of the wobble signal extracted from the band pass filter 107, a bias generating circuit 111 for generating the bias voltage, a low pass filter 112 for detecting the land pre-pit address from the output signal of the differential amplifying circuit 107, a land pre-pit detecting circuit 113 for detecting the land pre-pit address signal based on a certain voltage level as a comparison level, which is obtained by adding a generated voltage from the bias generating circuit 111 and an amplitude signal of the wobble signal, a land pre-pit address detecting circuit 114 for detecting the land pre-pit address from the land pre-pit binary signal detected at the land pre-pit detecting circuit 113, a reproduction signal binary-coding circuit 115 for binarizing a reproduction signal generated in the servo signal/reproduction signal generating circuit 104, a data reproducing PLL circuit 116 for generating clocks for demodulating the output signal of the reproduction signal binary-coding circuit 115, a demodulating circuit 117 for carrying out demodulation using the data and clocks generated by the data reproducing PLL circuit 116, an error correcting/adding circuit 118 for adding the correction code to user data received through interface of a personal computer, etc. connected to the apparatus 80 or correcting the demodulated data using the correction code at the time of data reproduction, and a modem control circuit 119 for transmitting the data with the error correction code added to a modulation circuit 120 or transmitting the data from the demodulation circuit 117 to the error correction/addition circuit 118 and for controlling the modulation circuit/demodulation circuit 117, 120.
Furthermore, the optical disc apparatus 80 comprises the modulation circuit 120 for modulating the user data to which the correction code is added, a laser drive waveform generating circuit 121 for generating the laser drive waveform from the output signal of the modulation circuit 120, a laser drive circuit 122 for driving the laser, a gate signal generating circuit 123 for generating the timing signal required for recording and reproducing the data. and a central processing unit (hereinafter referred to as “CPU”) 124 for controlling the overall apparatus 80.
Referring now to FIGS. 9A-9F, the operation of the optical disc apparatus 80 will be described. First of all, description will be made -on binary-coding of the land pre-pit address at the time of reproducing the information. FIGS. 9A-9F show waveforms of output signals from the tracking detectors when the optical disc apparatus 80 (FIG. 8) keeps tracking the guiding groove of the DVDR/RW format disc 101. The waveforms at the time of tracking an unrecorded track are shown in the right side of FIGS. 9A through 9F. Assume that the optical head 103 (FIG. 8) of the optical disc apparatus 80 is equipped with two. tracking detectors A and B (for example, see FIG. 2). Because the tracks on the disc are modulated in the radial direction, the light amount signals on the detector repeatedly increase and decrease at a predetermined frequency by the modulation. Furthermore, pulse-form detection signals are observed at a predetermined position of the modulated signal by the address information (i.e., land pre-pit address) recorded on the land section.
The differential amplifying circuit 106 (FIG. 8) of the optical disc apparatus 80 generates differential signals of FIGS. 9A and 9B. The differential signal is further passed to LPF 112 (FIG. 8) for removing noise of the high-pass components or reducing influence of recording signals at the time of recording. As a result, signals shown in FIG. 9C are obtained. For the detection level to detect the land-prepit address signal, a voltage level obtained by adding the signal amplitude voltage of the wobble signal extracted by the band pass filter 107 (FIG. 8) and a predetermined voltage generated by the bias generating circuit 111 (FIG. 8) is adopted. FIG. 9F shows the waveform of the land pre-pit binary-coded signal thus obtained. The LPP address detecting circuit 114 demodulates and detects the land pre-pit address based on the land pre-pit address signal, wobble binary-coded signal, and the clock signal generated at the wobble PLL.
Continuously referring to FIGS. 9A-9F, the operation when the optical disc apparatus 80 (FIG. 8) records the information is described. The waveforms when the information is recorded are shown with waveforms on the right side of FIGS. 9A through 9F. The optical disc apparatus 80 detects signals by reducing gains of the detecting circuit inside the optical head 103 (FIG. 8) which has a function for converting the current that flows the tracking detectors to the voltage in order to prevent the circuit from being saturated even at the high recording power at the time of recording.
When information is being recorded, the tracking detectors of the optical head 103 (FIG. 8) detects the recording signal. More precisely, the optical head 103 (FIG. 8) does not detect the wobble modulated signal and LPP address signal themselves, but detects the wobble modulated signal and LPP address mixed with recording signals. FIGS. 9A and 9B (when recording) indicate the light amount signals when detected by the tracking detectors A and B. The differential amplifying circuit 106 (FIG. 8) of the optical disc apparatus 80 generates differential signals shown in FIGS. 9A and 9B. FIG. 9C shows the signal waveform that passes the LPF 112 (FIG. 8). The LPF 112 (FIG. 8) is equipped for reducing the mixed recording signal. However, as shown in FIG. 9C, it is understood that influences of mixed recording signals remain in the signal waveforms after passing through the LPF 112 (FIG. 8).
Even in recording, the detection level of the land pre-pit is determined in such a manner so as to detect the land pre-pit address. As shown with a dotted line of FIG. 9C, the detection level is set nearly equivalent to the maximum amplitude level of the signal waveform with the recording signal mixed. However, with this configuration, a large number of pseudo-pulses are detected in the land pre-pit binary-coded signals (FIG. 9F). As a result, the detection ratio of LPP address at the LPP address detecting circuit 114 (FIG. 8) lowers. What must be taken into account is that the land pre-pit address detection ratio lowers when the detection level is increased in order to avoid erroneous detection. The reason is that at the low-power section when recording power modulation is carried out, the case in which the land pre-pit address is unable to detect occurs.
Furthermore, since in this detection system, the differential signal of the signals detected by the tracking detectors of the optical head 103 (FIG. 8) is used in order to detect the LPP address, the address detection ratio greatly varies in accordance with the off-track condition of the optical head 103. This is because, at the time of recording, the light amount signals reflected by the optical disc 101 (FIG. 8) and returned to the tracking detectors become unbalanced by the off-track condition, and the condition of the differential signal is greatly changed.
In addition, the tertiary feature of the above-mentioned format is that the information can be recorded by installments. According to this format, it is possible to additionally record the data by identifying the record initiating position by the processing called linking from the last section to which the information was recorded. The conventional optical disc apparatus 80 (FIG. 8) detects-track jumps at the time of recording based on the tracking error signal. The reason is that the address detection ratio at the time of recording is low and the danger of causing track jump, etc. and recording the data in other addresses must be avoided. However, when the track jump of the optical head is detected by using the tracking error signal, there may be misdetection. For example, the error signal is detected greatly due to eccentricity, etc. of the disc. To avoid such misdetections, a comparison level of the tracking error signal for determining whether a track jump has occurred or not should be set higher in order to properly detect track jumps. Thus, it is important to increase the address detection ratio.
Since in the conventional optical disc apparatus 80 (FIG. 8) the LPP address detection ratio during recording or reproducing the recorded tracks lowers, there are not many methods to detect whether or not the apparatus was recording the data in the correct track by detecting a primarily tracking error signal, and especially, the reliability during recording was low. In addition, depending on the off-track condition of the optical head, there was a problem of further lowering the LPP address detection ratio.